The impressive rank - and a spot on the NSW all-round achievers list for scoring more than 90 per cent in all her subjects - left the Figtree student jumping for joy.

"I wasn't expecting to get 99, but I definitely worked towards the all-rounders all year, so I'm very happy about that," she said.

Her advanced mathematics mark of 99 meant she ranked sixth in NSW for the subject.

Alongside her academic work, Siobhan kept up a strong social and sporting schedule of netball, competitive swimming, physical culture, running and attending the surf club.

"I worked really hard but I think it was all the other stuff that helped the most, especially my sport, because I had good time management and motivation - and maybe I was pretty competitive too," she said.

She also managed to come first in all of her subjects at St Mary's, making her dux of the school, and received the St Mary's Award, which also recognised her efforts in tutoring younger students, volunteering for charity and being a role model in all areas at school.